1. Field of the Invention
The present invention relates to an improved hydrocracking process. It particularly relates to a combination hydrorefining, heat-treating and hydrocracking process.
2. Description of the Prior Art
Hydrocracking is a well known process for upgrading hydrocarbon fractions. See, for example, Hydrocarbon Processing, Sept. 1976, pages 121-128. In the hydrocracking process, a hydrocarbonaceous oil is contacted in the presence of added hydrogen and a hydrocracking catalyst to produce lower boiling hydrocarbons. When the hydrocarbonaceous oil feed for the hydrocracking process comprises a high nitrogen content, the feed is usually hydrorefined in the presence of added hydrogen and a hydrorefining catalyst to decrease the nitrogen content of the feed prior to the hydrocracking stage.
U.S. Pat. No. 3,055,823 discloses a process which comprises hydrorefining a petroleum distillate boiling in the range of 200.degree. to 850.degree. F., preferably in the range of 325.degree. to 650.degree. F. to denitrify the distillate, removing ammonia from the hydrorefined effluent, heat treating the remaining hydrorefined effluent, and hydrocracking the heat treated effluent. In the heat treating zone, the hydrorefined effluent is passed through a siliceous cracking catalyst at conditions below which significant cracking occurs, i.e. below 650.degree. F.
It has now been found that a specific sequence, including an intermediate heat treatment in the presence of hydrogen, will increase the selectivity of the hydrocracked product to components boiling in the range of about 350.degree. to 675.degree. F., i.e. components boiling in the jet fuel and diesel fuel ranges, when hydrocracking a feed boiling above 650.degree. F.